CHARACTERIZATION OF STRAY ELECTRIC-FIELDS IN NIOBIUM CAVITIES USING ULTRA-HIGH-RESOLUTION SPECTROSCOPY

We present the results of an experiment in which the stray fields in a niobium probe were measured. This probe simulated the entrance/exit h oles of a high-Q cylindrical cavity (micromaser in Garching) where int erference effects, attributed to these stray fields, have been observe d [Raithel et al., Phys. Rev. Lett. 75 (1995) 3446]. The gradient of t he stray electric fields was measured in both the metallic and superco nducting phases with ultra high resolution spectroscopy which used a c ombination of the Doppler free two photon method and the technique of successive oscillatory fields, We obtain a value of 300 mV/cm for the electric field for both phases which is in excellent agreement with th e determination of Raithel et al. (C) 1997 Elsevier Science B.V.